It looks like the Saga of the Unlocked BCLK is coming to a bursting conclusion with both ASUS and ASRock enabling overclocking the base clock frequency of non-K Skylake processors. From the looks of it, a simple BIOS trick will enable the overclocking capabilities.

Update #1: Elmor posted a bit more details on the unlocking in the forum. For now the BCLK unlocking is in experimental stage with most obvious drawbacks being the lack of power management functionality and some benchmarks like XTU not working properly. The BIOSes will arrive in the coming days as more fin-tuning is required.

Update #3: after ASRock now also ASUS and MSI have uploaded BIOSes for their Z170 motherboards. Elmor has uploaded the BIOSes for 7 motherboards: Maximus VIII Hero, Maximus VIII Gene, Maximus VIII Extreme, Maximus VIII Impact, Z170-DELUXE, Z170-A and Z170-E. Note that these are in fact BETA versions of the BIOS and there is thus a long list of issues and warnings: no IGPU, No dynamic change of CPU frequency, No C-states, No Turbo Mode, CPU temperature reading is incorrect, AVX instructions have very low performance and Windows XP ACPI not supported. You can download the BIOSes here.

In the MSI Z170A XPOWER GAMING Titanium Edition official support thread, Pepinorang has also uploaded the non-K OC BIOS for the (duh!) XPower motherboard. The washlist of issues includes the same as mentioned above. You can download the BIOS here.